Sweet spot for 4.10 gears

[ACZL]

I've got the bullet proof vest on, shields up and ready. If this has been asked countless times before, I apologize in advance. What is the sweet spot for towing if truck has 4.10 gears and diesel? Test drove a '17 F350 that had 'em and at 60 mph, rom's were around 1850+/-. 70 mph = around 2150 +/-. Obviously compared to 3.55 gears about 300 rpm's more on both accounts.

[Cummins12V98]

Campinghoss@51 wrote:
To me I don't worry about sweet spots, fuel efficiency or stuff like that. I always pull at 65 mph and when the fuel gauge reads 1/4 empty fill her up. I am not being critical to those who do as everyone has things they like to think about. I had to think a lot when I was working. Now I enjoy chilling! :B

I agree!!! But don't tow at 65 in CA!!! They will allow 60.

[Campinghoss]

To me I don't worry about sweet spots, fuel efficiency or stuff like that. I always pull at 65 mph and when the fuel gauge reads 1/4 empty fill her up. I am not being critical to those who do as everyone has things they like to think about. I had to think a lot when I was working. Now I enjoy chilling! :B

[Travlingman]

4x4ord wrote:

Travlingman wrote:
When I was trying to decide on 3.55's or 4.10's a guy on the Ford forum figured out the different RPM's for the ratios and RPM's. Here it is.

4.10 DRW
4th gear 55 = 2764; 60 = 3015
5th gear 55 = 2061; 60 = 2248; 65 = 2435; 70 = 2622
6th gear 55 = 1624; 60 = 1772; 65 = 1919; 70 = 2067
Sweet spot for climbing: 64 - 75

3.55 DRW
4th gear 55 = 2393; 60 = 2610; 65 = 2828
5th gear 55 = 1784; 60 = 1946; 65 = 2108; 70 = 2271; 75 = 2433
6th gear 55 = 1406; 60 = 1534; 65 = 1662; 70 = 1790
Sweet spot for climbing: 55 - 64; > 74

He considered the sweet spot for climbing the big hills to be in the 2400 - 2800 RPM range.

I went with 4.10's and his figures appear right to me from my driving/towing experience.

2400-2800 rpm may be the sweet spot for towing hills. The thing is you need to factor in your weight and the slope of the grade to be able to know how fast the engine can tow your trailer up the hill.
Just guessing your truck and trailer combined might weigh in at about 25000 lbs.

If you are wanting to tow your trailer up 6% grades you can easily calculate that the rear wheel power required to overcome the grade:

.06 x 5280 ft in a mile = 317 feet per mile.

At 65 mph your going to travel that mile in 55 seconds.

So you need to be able to lift 25000 lbs 317 feet in 55 seconds.

1 Hp is the power required to lift 550 lbs 1 ft in 1 second.

Therefore: (317 x 25000 ÷ 55)/550 = 262 HP

Additionally you can expect that it will take roughly 100 rear wheel hp to overcome wind and rolling resistance at 65 mph.

The rear wheel hp required to tow your trailer up a 6% grade at 65 mph is 362 hp.

Power is lost to heat in the rear end and transmission as and there is power required to run things like your cooking fan a/c and alternator. To get 362 hp to the rear wheels your engine would be required to make much more than 362 hp.

It's kind of a guess but it you assume an efficiency of 75% your not going to be too far off. This means that to put 362 hp to the rear wheels your engine would need to produce 482 HP. That's not going to happen. At 2400 rpm The 2017 Powerstroke will make about 395 HP.

Your going to be pulling 6% grades at speeds closer to 55 mph. So according to what your friend calculated you will be in 4th gear at 2800 rpm which is great. The 3.55 gear ratio would also be in the zone at 2400 rpm.


And on a little steeper grade the 4.10 would shine but on a little less grade the 3.55 would shine. As the grade approaches 8% the 3.55 equipped truck will our perform the 4.10 again. Fuel economy will go to 3.55 gears.

You are correct, I scale right at 25,000 Lbs. But I guess my truck must have failed math, as I run I-26 through TN/NC border, Sams Gap, Buckner Gap and then the Saluda Grade NC/SC line alot. All 6% grades or better and run right at 65 MPH in 5th gear at 2400/2500 RPM's.

[wilber1]

Cummins12V98 wrote:
^^^^^^^ Dude where the HE!! does all that info come from??? Your brain must be very cluttered.

I tow mostly at 60 in 6th at 1,750 rpm's combined 33k average all conditions 9mpg. Any faster I get worse mileage. Any slower I get better. Less clutter in my brain. :B

True, mechanical losses and drag increase with RPM and speed. WOT calculations are only useful if operating at WOT, which none of us do unless climbing steep grades. At least I don't.

With turbo diesels with quite flat torque curves, if you stay some ways into the fattest part of the curve, HP differences will be smaller with changes in RPM. That's my theory anyway.

[4x4ord]

Thanks Cummins. I didn't take it in any way to be offensive.

[Cummins12V98]

I have towed HEAVY with 3.42's @ 29K and 4.10's @ 33-35K combined. Towing 29K or less go with the 3.42's as you can run 5th basically the same rpm as the 4.10's in 6th with the bonus much better solo mileage.

4x4ord, what I said earlier about you was a compliment!

[4x4ord]

Travlingman wrote:
When I was trying to decide on 3.55's or 4.10's a guy on the Ford forum figured out the different RPM's for the ratios and RPM's. Here it is.

4.10 DRW
4th gear 55 = 2764; 60 = 3015
5th gear 55 = 2061; 60 = 2248; 65 = 2435; 70 = 2622
6th gear 55 = 1624; 60 = 1772; 65 = 1919; 70 = 2067
Sweet spot for climbing: 64 - 75

3.55 DRW
4th gear 55 = 2393; 60 = 2610; 65 = 2828
5th gear 55 = 1784; 60 = 1946; 65 = 2108; 70 = 2271; 75 = 2433
6th gear 55 = 1406; 60 = 1534; 65 = 1662; 70 = 1790
Sweet spot for climbing: 55 - 64; > 74

He considered the sweet spot for climbing the big hills to be in the 2400 - 2800 RPM range.

I went with 4.10's and his figures appear right to me from my driving/towing experience.

2400-2800 rpm may be the sweet spot for towing hills. The thing is you need to factor in your weight and the slope of the grade to be able to know how fast the engine can tow your trailer up the hill.
Just guessing your truck and trailer combined might weigh in at about 25000 lbs.

If you are wanting to tow your trailer up 6% grades you can easily calculate that the rear wheel power required to overcome the grade:

.06 x 5280 ft in a mile = 317 feet per mile.

At 65 mph your going to travel that mile in 55 seconds.

So you need to be able to lift 25000 lbs 317 feet in 55 seconds.

1 Hp is the power required to lift 550 lbs 1 ft in 1 second.

Therefore: (317 x 25000 ÷ 55)/550 = 262 HP

Additionally you can expect that it will take roughly 100 rear wheel hp to overcome wind and rolling resistance at 65 mph.

The rear wheel hp required to tow your trailer up a 6% grade at 65 mph is 362 hp.

Power is lost to heat in the rear end and transmission as and there is power required to run things like your cooking fan a/c and alternator. To get 362 hp to the rear wheels your engine would be required to make much more than 362 hp.

It's kind of a guess but it you assume an efficiency of 75% your not going to be too far off. This means that to put 362 hp to the rear wheels your engine would need to produce 482 HP. That's not going to happen. At 2400 rpm The 2017 Powerstroke will make about 395 HP.

Your going to be pulling 6% grades at speeds closer to 55 mph. So according to what your friend calculated you will be in 4th gear at 2800 rpm which is great. The 3.55 gear ratio would also be in the zone at 2400 rpm.


And on a little steeper grade the 4.10 would shine but on a little less grade the 3.55 would shine. As the grade approaches 8% the 3.55 equipped truck will our perform the 4.10 again. Fuel economy will go to 3.55 gears.

[Turtle_n_Peeps]

4x4ord wrote:

dodge guy wrote:


Yes he has been trying to convince people that lower gearing is better for towing.

All his rambling makes him sound like an engineer. They think they know everything on paper, but in the real world things are hugely different.

People will be smart to avoid his “recommendations”!

I am not advocating that taller gear ratios are better for towing. I am advocating that engineers recommend the best gear ratio based on the expected use of the truck. The heavier the trailer the deeper the ratio you need but if you don't have a heavy trailer the deeper gears can be detrimental to both fuel economy and towing performance. Deeper is not simply better than taller... Taller is better for lighter trailers. These trucks are designed to tow over 30,000 lbs so most RVs fall in the lighter trailer category.

^^^^ good post and spot on.

IOW's the more HP an engine puts out the less gear you need.

[Travlingman]

When I was trying to decide on 3.55's or 4.10's a guy on the Ford forum figured out the different RPM's for the ratios and RPM's. Here it is.

4.10 DRW
4th gear 55 = 2764; 60 = 3015
5th gear 55 = 2061; 60 = 2248; 65 = 2435; 70 = 2622
6th gear 55 = 1624; 60 = 1772; 65 = 1919; 70 = 2067
Sweet spot for climbing: 64 - 75

3.55 DRW
4th gear 55 = 2393; 60 = 2610; 65 = 2828
5th gear 55 = 1784; 60 = 1946; 65 = 2108; 70 = 2271; 75 = 2433
6th gear 55 = 1406; 60 = 1534; 65 = 1662; 70 = 1790
Sweet spot for climbing: 55 - 64; > 74

He considered the sweet spot for climbing the big hills to be in the 2400 - 2800 RPM range.

I went with 4.10's and his figures appear right to me from my driving/towing experience.

[4x4ord]

dodge guy wrote:


Yes he has been trying to convince people that lower gearing is better for towing.

All his rambling makes him sound like an engineer. They think they know everything on paper, but in the real world things are hugely different.

People will be smart to avoid his “recommendations”!

I am not advocating that taller gear ratios are better for towing. I am advocating that engineers recommend the best gear ratio based on the expected use of the truck. The heavier the trailer the deeper the ratio you need but if you don't have a heavy trailer the deeper gears can be detrimental to both fuel economy and towing performance. Deeper is not simply better than taller... Taller is better for lighter trailers. These trucks are designed to tow over 30,000 lbs so most RVs fall in the lighter trailer category.

[bucky]

I'm thinking the availability of 925 ft lbs means the whole range of rpm is the sweet spot eh?

[dodge_guy]

Cummins12V98 wrote:
^^^^^^^ Dude where the HE!! does all that info come from??? Your brain must be very cluttered.

I tow mostly at 60 in 6th at 1,750 rpm's combined 33k average all conditions 9mpg. Any faster I get worse mileage. Any slower I get better. Less clutter in my brain. :B

Yes he has been trying to convince people that lower gearing is better for towing.

All his rambling makes him sound like an engineer. They think they know everything on paper, but in the real world things are hugely different.

People will be smart to avoid his “recommendations”!

[Rbertalotto]

4x4....that explanation was fantastic. Best I’ve seen on torque vs hp with regard to RPM and fuel consumption. I copied it for future reference. Thank you!

[4x4ord]

If you're burning 1 gallon per 9 miles and travelling 60 mph you're burning 6.67 gallons per hour. Because diesel contains 55 hp hrs per gallon you're engine is releasing 367 hp. If it is 40% efficient the usable power produced is 147 hp. So 147 hp is a good guess as to the average power required to tow you're trailer down the highway at 60 mph.